The Effect of Dielectric Coating on the Local Electric Field Enhancement of Au-Ag Core-Shell Nanoparticles

The plasmon-induced local electric field enhancement of Au-Ag nanoshell could be fine tuned by dielectric coating. Theoretical calculation results indicate that the anti-bonding plasmon-induced local field peak at a shorter wavelength always fades down as the dielectric coating thickness is increased. For bonding plasmon-induced local field peak at a longer wavelength, the dielectric coating thickness-dependent monotonic intensity decrease only takes place when the Au-Ag nanoshell has a very small or very large gold core. Because of the competition between the distance-dependent field reduction and dielectric polarization-induced field enhancement, nonmonotonic intensity change could be observed for bonding plasmon-induced local field effect. By choosing an appropriate value of the gold core radius, the local field could be enhanced firstly and then fades down, and the maximum local field enhancement could be further enhanced by increasing the dielectric constant of the coating layer. The obtained results present a potential application in the molecule binding participant surface-enhanced fluorescence and surface-enhanced Raman scattering (SERS).